A significant cost in the manufacture of devices such as high speed photodetectors and solar cells based on III-V class semiconductor materials is the cost of Ge substrates on which the III-V class semiconductor materials can be grown by epitaxy. As a more cost effective alternative, Ge layers have been grown on Si substrates to form virtual Ge substrates which then form the basis for epitaxial growth of the III-V class semiconductor materials. However, known heteroepitaxy methods of growing such Ge layers on Si wafer substrates require ultra-high vacuum conditions and the use of costly and extremely toxic germane gas.
Further, such methods often result in the Ge layer having a sub-optimal surface roughness and a threading dislocation density that may require post processing to improve the quality of the Ge layer.
Still further, to obtain a suitable Ge surface for growth of the III-V class semiconductor materials, a transition layer several micrometers thick and comprising a mixture of Ge and Si is typically required. The small bandgap and the strong photon absorption of Ge prevent that for such a thick Ge layer the underlying Si substrate can include a functioning Si cell.
There exists a need for technological advancement.